Hardening and/or tempering furnace for self-hardening steel alloys and high-speed steels

ABSTRACT

A furnace for hardening self-hardening steel alloys and highspeed steels comprises a chamber with double walls of refractory material such as quartz. A piece to be hardened is held in the chamber in an atmosphere of inert gas. Heating means bring the temperature in the chamber up to the hardening temperature of the piece which is then abruptly cooled by circulating cooling water between the double walls. An oil hardening bath may be located below the chamber so that air hardening, drawing and tempering as well as oil hardening can all be carried out with the same installation.

United States Patent Beguin et a1.

[54] HARDENING AND/OR TEMPERING FURNACE FOR SELF-HARDENING STEEL ALLOYS AND HIGH-SPEED STEELS lnventors: Claude P. Beguin; Jean-Pierre F. Betrix,

both of Peseux, Switzerland Assignec: Borcl S. A., Pescux, Switzerland Filed: Feb. 3, 1970 Appl. No.: 8,374

Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 1,185,280 5/1916 Beardsley ..266/5 C 1,453,358 5/1923 Kettering..... ...266/5 E 1,994,629 3/1935 Arkema ..266/5 C 3,475,014 10/1969 Frank et al.. ...266/4 E 2,755,506 7/1956 Weber ....165/64 1,747,934 2/1930 Heidenhain ..266/5 E Primary Examiner-Gerald A. Dost Att0rneyRobert E. Burns and Emmanuel .l Lobato [57] ABSTRACT A furnace for hardening self-hardening steel alloys and highspeed steels comprises a chamber with double walls of refractory material such as quartz. A piece to be hardened is held in the chamber in an atmosphere of inert gas. Heating means bring the temperature in the chamber up to the hardening temperature of the piece which is then abruptly cooled by circulating cooling water between the double walls. An oil hardening bath may be located below the chamber so that air hardening, drawing and tempering as well as oil hardening can all be carried out with the same installation.

8 Claims, 2 Drawing Figures Patented Feb. 29, 1972 3,645,518

2 Sheets-Sheet l Patented Feb. 29, 1972 2 Sheets-Sheet 2 then to a cooling zone, are known. This movement necessitates handling and driving means such as a travelling belt or a chain, or a metal bar which must enter the furnace.

The necessity of providing these driving means obviously results in a major drawback. An object of the present invention is to remove this drawback by uniting the successive zones into a single zone in which the part to be hardened can remain static.

According to the invention there is provided a furnace for hardening self-hardening steel alloys and high-speed steels comprising a chamber with double walls of refractory material,'means for manufacturing an atmosphere of an inert protective gas in said chamber, means for heating said chamber at least up to hardening temperature of a piece of selfhardening steel alloys or high-speed steel contained in said chamber, and means for circulating a cooling fluid between said double walls.

The accompanying drawings show, by way of example, two embodiments of the invention.

F 10. 1 is a schematic diagram of a first embodiment.

FIG. 2 is a schematic cross section of a second embodiment.

FIG. 1 schematically shows a furnace for the tempering of self-hardening steel alloys and high-speed steels comprising an enclosed heating space 1, heated electrically, by gas or oil, and surrounding a quartz tube 2 with a double wall 3 and 4, between which cooling water can circulate entering by an inlet conduit 5 and drained through an outlet conduit 6. The water supply circuit comprises a pump 7, an electromagnetic drain valve 8, a water reserve 9, an ion charger 10, and a cooling spiral coil 11.

The upper part of the quartz chamber 2 is shut off by a clos ing device 12 comprising a cooler 13 with circulating water, a

cover 14 which supports radiation screens 15, a gas inlet pipe 16, and a gas outlet pipe 17.

The gas supply passes from a constant pressure gas reservoir 18 through a flow meter 19, a needle-valve 20, and an electromagnetic bypass valve 21. The closing device 12 addi tionally carries a support 22 for the parts to be hardened which are placed in the quartz enclosure. This support 22 can have the form of rods from which the parts are suspended or a plate on which they are placed. A metal cage 23 prevents any contact between the parts and the wall of the quartz enclosure.

The installation is completed by electrical regulating and control devices comprising a programmed regulator controlling the increase in temperature of the furnace and a control device able, at the moment of chilling to simultaneously switch off the furnace, turn on the water flow between the walls 3, and open valve 21 ensuring a strong inflow of gas to the enclosure.

As quartz is able to sustain very violent thermic shocks, the water can be fed in when the part to be tempered has reached the hardening temperature of about 1,000 C. for self-hardening steel alloys and 1,200 C. to l,300 C., for high-speed steels.

The furnace is used in the following manner: with the furnace cold, the parts to be hardened are suspended from the cover 14 by means of the support 22 then the cover 14 is fastened to the quartz tube 2 and water is circulated through cooler 13. Enclosure 2 is next purged with gas, the latter passing through the needle valve 20. A slight flow of gas is maintained throughout the treatment.

The furnace is next put into operation, the temperature increase curve being controlled by the programmed regulator. When the hardening temperature is reached, the three following operations are simultaneously triggered: heating is stopped, pump 7 which forces the water between the walls 3 and 4 is started, and a strong stream of gas is injected by the opening of electromagnetic valve 21.

When the pieces are chilled (or hardened) the flow of gas is decreased by closing valve 21. Water continues to run between walls 3 and 4 until the furnace is about C. lower than the tempering or drawing temperature. The water is next drawn off by opening electromagnetic: valve 8, and the furnace is heated to the tempering or drawing temperature. When the drawing or tempering is terminated pump 7 is started which again forces water between walls 3 and 41 and allows the parts to cool.

Numerous variations are obviously possible, particularly in the circulation and water cooling circuit which can comprise a heat exchanger and a fan. instead of quartz it is possible to employ other refractory materials capable of resisting strong thermic shocks.

The furnace heretofore described offers the advantage of requiring no handling and driving device for the parts to be treated. In fact, while other known furnaces are divided into several compartments at different temperatures each intended for separate operations, the above-described furnace is only provided with one chamber which has a fluidtight enclosure and is therefore not suitable for oil hardening since the part to be treated cannot be quickly transferred into an oil bath outside the furnace. Known furnaces do not permit, without modification of the equipment, any form of hardening on one piece and the passing to another form of this treatment for another piece. In the second embodiment it is possible to harden self-hardening steel alloys and high-speed steel as well as oil-hardening steels in the same furnace.

FIG. 2 of the drawing diagrammatically shows a furnace intended for oil-hardening comprising a vertical cylindrical heating chamber 1 surrounding a tube 2 made in a refractory material which can support a strong thermic shock such as quartz. The tube has a double wall 3 and 41 between which cooling water can circulate, entering by inlet 25 and draining by outlet 26. This tube, protected internally by a metal cage 27 whichprevents contact between the part to be hardened and the refractory material, is closed by cover 28 at the upper part thereof and at its lower part by a horizontal metal slide valve 29 housed in a waterproof case 30 which is attached to the vertical tube 2 by a stuffing-box. Cover 28 has an aperture allowing passage for gas inlet 31 and additionally supports radiation screens 32. The suspension rod 34 on which the parts to be treated are suspended and driven by the mechanisms 35 is guided by means of a stuffing-box 33 placed inside the cover 28. With the exception of the operating device for the movement of the parts, the furnace thus described is the same as the furnace illustrated in FIG. 1. When the slide valve 29 is opened a tube 36 having the same properties as tube 2 opens into and extends tube 2. Tube 36 dips into an oil circulating bath 37 and comprises a gas outlet 38, connected to gas outlet 39 situated at the lower extremity of the principal tube 2. The circulation of the oil in the bath is ensured by pump 40, the oil inlet pipe to the bath being surmounted by a cylindrical funnel 41, placed under a receptacle 42 for the parts to be hardened in oil, thus allowing the liquid to wash vertically subject to the flow at a certain speed around and through said receptacle.

Whatever the method of hardening to be carried out, the following conditions always apply: with the furnace cold and the slide valve in the closed position, the parts to be treated are attached to the suspension rod 34. From the time cover 28 is fixed onto tube 2, a weak flow of protective gas is then sent into the latter by means of pipe 11, this How being maintained throughout the treatment. Next the Ifumace is started up and the increase in temperature, controlled by the programmed regulator, ensures a minimum deformation and avoids any risk of fissures being formed in the part to be treated. in order to harden self-hardening steel alloy and high-speed steel, once the hardening temperature is reached, the heating is cut off, cooling water is introduced between walls 3 and d of tube 2,

and a strong stream of gas is injected and the drawing or tempering procedure is completed as before. On the other hand, for oil hardening of steel, at the end of the heating period, three operations are put into effect simultaneously: tubes 2 and 36 are connected up by opening the slide valve 29, the slide being intended to cut the radiation on the oil, the oil pump started and the vertical descent of the parts towards the receptacle 42 caused. A weak flow of protective gas is maintained; in fact, by circulating the gas from top to bottom, this prevents oil vapor mounting into the heated part of the tube. The gas which, before the opening of the slide valve 29, was evacuated by conduit 39 is then also evacuated by conduit 38 placed in the bottom part of the tube 36. The great advantage of the furnace heretofore described is that it enables both the hardening, drawing or tempering of self-hardening steel and the oil hardening of steel. With reference to the furnace shown in FIG. I, the only alterations are the addition of a fluidtight casing 30 extended by a tube 36, comprising a slide valve 29 and in the introduction of means for vertically moving the parts to be treated. But this movement, whilst it is necessary during oil hardening is never used for the other methods of hardening. Thus, the determining improvement brought out by the first embodiment still remains: when self-hardening steel alloys and steel are to be hardened, the parts remain static in relation to the furnace.

What is claimed is:

l. Furnace for hardening self-hardening steel alloys and high-speed steels comprising a chamber with double walls of refractory material transparent to radiant heat, closure means for said chamber, means for maintaining an atmosphere of an inert protective gas in said chamber, heating means outside said double walls for heating by radiation transmitted through said double walls, a piece of self-hardening steel alloy or highspeed steel contained in said chamber at least up to the hardening temperature of said piece, and means for thereafter circulating a cooling liquid between said double walls to cool said piece.

2. Furnace according to claim 1, wherein said refractory material of said double walls is quartz.

3. Furnace according to claim 1, wherein said chamber is closed at the lower part thereof by an openable baffle plate and wherein at least the inner of said double walls is extended below said bafile plate into a bath in which oil can be circulated, and comprising means for lowering said piece from said chamber into said oil bath.

4. Furnace according to claim 3, wherein said chamber has an inlet for said inert protective gas at the upper part of said chamber an outlet for said gas at the lower part of said chamber above said baffle plate, and an outlet for said gas in said extension below said baffle plate.

5. Furnace according to claim 1, further comprising cage means for preventing contact between said piece and said double walls while permitting passage of said radiant heat from said heating means to said piece.

6. Furnace according to claim 1, wherein said closure means comprises radiation screens to inhibit radiation from said chamber.

7. Furnace according to claim I, comprising means for suspending said closure means.

8. Furnace according to claim 1, wherein said means for maintaining an atmosphere of inert gas in said chamber comprises gas inlet and outlet passages in said closure means. 

1. Furnace for hardening self-hardening steel alloys and highspeed steels comprising a chamber with double walls of refractory material transparent to radiant heat, closure means for said chamber, means for maintaining an atmosphere of an inert protective gas in said chamber, heating means outside said double walls for heating by radiation transmitted through said double walls, a piece of self-hardening steel alloy or high-speed steel contained in said chamber at least up to the hardening temperature of said piece, and means for thereafter circulating a cooling liquid between said double walls to cool said piece.
 2. Furnace according to claim 1, wherein said refractory material of said double walls is quartz.
 3. Furnace according to claim 1, wherein said chamber is closed at the lower part thereof by an openable baffle plate and wherein at least the inner of said double walls is extended below said baffle plate intO a bath in which oil can be circulated, and comprising means for lowering said piece from said chamber into said oil bath.
 4. Furnace according to claim 3, wherein said chamber has an inlet for said inert protective gas at the upper part of said chamber an outlet for said gas at the lower part of said chamber above said baffle plate, and an outlet for said gas in said extension below said baffle plate.
 5. Furnace according to claim 1, further comprising cage means for preventing contact between said piece and said double walls while permitting passage of said radiant heat from said heating means to said piece.
 6. Furnace according to claim 1, wherein said closure means comprises radiation screens to inhibit radiation from said chamber.
 7. Furnace according to claim 1, comprising means for suspending said closure means.
 8. Furnace according to claim 1, wherein said means for maintaining an atmosphere of inert gas in said chamber comprises gas inlet and outlet passages in said closure means. 